1. Field of the Invention
This invention relates to a pyridine-based compound and a metal complex containing the pyridine-based compound, and particularly to a 2-phenyl-6-azolylpyridine-based ligand and a Group VIII transition metal complex containing the 2-phenyl-6-azolylpyridine-based ligand.
2. Description of the Related Art
In recent years, solar cells have been developed with the increasing demand for energy. In particular, the dye-sensitized solar cells have been most promise among solar cells. The dye-sensitized solar cells absorb visible light and near infrared light to excite electrons. The excited electrons are effectively transferred to a conduction band of a semiconductor in the dye-sensitized solar cells to generate a photocurrent. Therefore, the property of a dye used in the dye-sensitized solar cells will affect directly the photoelectric conversion efficiency of the dye-sensitized solar cell. At present, the ruthenium complex is the main target of research for the dye in the solar cell.
U.S. Pat. No. 7,790,980 discloses a dye comprising a Group VIII transition metal complex represented by the following formula (1):M1(T1)m1(T2)m2G1m3G2m4  (1)
wherein, M1 represents Group VIII transition metal complex; each of T1 and T2 is independently selected from ligands represented by the following formula (1a):

In formula (1a), n is either 0 or 1, each of r1, r2 and r3 is independently selected from the group consisting of: —COOH, —PO3H, —SO3H, —CO2−, —PO3−, —SO3−, a C1˜C20 substituted alkyl group, a C1-C20 unsubstituted alkyl groups, a C6-C30 substituted aryl group, a C6-C30 unsubstituted aryl group, a C6-C30 substituted aryloxy group, a C6-C30 unsubstituted aryloxy group, a C6-C30 substituted arylene group, a C6-C30 unsubstituted arylene group, a C1-C20 substituted alkylene group, a C1-C20 unsubstituted alkylene group, a C1-C20 substituted alkyleneoxy group, and a C1-C20 unsubstituted alkyleneoxy group;
G1 is selected from the group consisting of: hydrogen, NO2, Cl, Br, I, CN, NCS, H2O, NH3, Cl−, Br−, I−, CN−, NCS−, and PF6−;
G2 is selected from the group consisting of imidazolium cations, pyridinium cations, pyrrolidinium cations, and quinolidinium cations; and
each of m1 and m3 is an integer ranging from 0 to 3; m2 is an integer ranging from 1 to 3; and m4 is an integer ranging from 1 to 6.
However, the photoelectric conversion efficiency of the metal complex in U.S. Pat. No. 7,790,980 and the absorption of the same in the visible light region and near infrared light region are insufficient. In addition, in exemplary examples of U.S. Pat. No. 7,790,980, because the metal complex includes two thiocyanate (NCS) ligands having weaker ligand bonding strength, chelation of the ligands with ruthenium is weak and unstable, thereby resulting in poor photoelectric conversion efficiency and short lifespan of the dye-sensitized solar cell.